Field of the Invention
The present invention relates to a robot apparatus, and a measuring method of a rotation driving apparatus.
Description of the Related Art
Conventionally, various robot apparatuses have been used in production sites of workpieces such as industrial products and the like. Recently, a robot apparatus or a robot system which is equipped with a multi-shaft multi-joint robot arm capable of performing more complicated operations is spreading. For example, a production line in which workpieces such as industrial products and the like are manufactured by using a so-called robot cell constituted by combining a plurality of robot apparatuses is known.
The constitution of the robot arm of the robot apparatus like this to be used for industrial purposes is sometimes classified into a vertical multi-joint constitution, a horizontal multi-joint constitution and the like, in accordance with the structure consisting of links and joints thereof. However, in any arm constitution, the basic constructions of the joints are similar to others. More specifically, the constitution of transmitting the output of a rotation driving source to the rotation shaft (or axis) of the driven-side link via a transmission (a speed reducer in many cases) is used.
Particularly, in the production line of the robot cell constitution, when the lifetime of one of the robot apparatuses included in the production line has come, it is necessary to suspend the manufacturing process and immediately take measures such as exchange of the relevant robot apparatus or the like. In general, it should be noted that the lifetime of the robot arm depends on the lifetime of the transmission (the speed reducer in many cases) used in the joint of the robot arm.
For this reason, in the workpiece (article) production system for which the robot apparatus is used, means for accurately diagnosing the lifetime of the transmission (speed reducer) of the robot arm has been desired. More specifically, if it is possible to estimate life expectancy of the transmission, then it is conceivable to be able to incorporate preventive measures such as assembly exchange of the joint, exchange for a new robot arm or an overhauled robot arm, and the like, into a production schedule. Thus, it is possible to prevent that the production line is suspended or stopped due to a sudden breakdown (coming of lifetime) of the robot arm.
In consideration of such situations as above, various techniques related to such lifetime diagnosis of the robot arm have been proposed recently. More specifically, the technique of measuring a wear amount of the gear of each joint, and then deciding the lifetime of the robot arm by converting the measured wear amount into a looseness amount at the arm end position has been proposed (for example, Japanese Patent No. 3089915). Besides, the technique of detecting and correcting a lost motion of the rotation driving system (due to looseness and/or hysteresis of the driving unit) by using the machine-end encoder and the motor encoder has been proposed (for example, Japanese Patent Application Laid-Open No. 2001-166805).
However, in case of measuring the wear amount of the gear by the technique described in Japanese Patent No. 3089915, it is necessary to once stop the robot arm and then measure the wear amount of the gear from the outside of the robot arm, and thus a manufacture interruption period due to time necessary for the measurement tends to be prolonged. Moreover, it may be necessary to take the robot arm apart in some cases. At that time, there is a problem that more operation time becomes necessary.
Moreover, Japanese Patent Application Laid-Open No. 2001-166805 discloses the constitution of measuring the lost motion by using the output-end encoder (machine-end encoder) and the input-end encoder (motor encoder) of the driving system such as a rack and pinion. Basically, it is conceivable that a similar measuring method can be applied to a rotation driving system of the joint of a vertical multi-joint (multi-shaft) robot arm. However, in a multi-shaft multi-joint robot arm, there is a possibility that a dynamic (mechanical) condition related to a measurement-target joint (the rotation driving system thereof) variously changes according to, for example, the orientation (position) of the arm, and such a change influences a measurement result. For this reason, it is difficult only by simply carrying out the measuring system described in Japanese Patent Application Laid-Open No. 2001-166805 to achieve high-reliability and high-accuracy lost motion measurement.